It happened on Grenfell Street, in the area of Kenilworth Avenue North and Nikola Tesla Boulevard, shortly before 11:30 p.m. Saturday.
Speaking to reporters Sunday morning, Claudio Mostacci, the Hamilton Fire Department’s public information officer, said fire crews found heavy black smoke and flames coming from the residence when they first arrived on scene.
“Crews immediately went inside to do their search and rescue. They did encounter additional individuals inside,” Mostacci said.
Three people were pronounced dead at the scene and three others, two occupants of the home and a neighbour, were taken to hospital for treatment.
“When we arrived on scene, a neighbour had gone inside the building to assist, to try to get people out but was not successful in getting to the people upstairs,” Mostacci added.
The fire, Mostacci said, was quickly knocked down.
“As (one crew) did their search and rescue, another crew did an interior attack, an aggressive interior attack and were able to knock the fire down,” he noted.
The cause of the fire is not yet known.
Investigators with the Office of the Fire Marshal will be on scene Sunday.
“We have a critical stress team that has already been dispatched to the individuals who were involved inside who came across the fatalities,” Mostacci said.